linux-kernel - [PATCH] iio: adc: at91: disable adc channel interrupt in timeout case

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Date:   Wed, 30 Jan 2019 14:42:02 +0100
From:   <g.ottinger@...tec.at>
To:     unlisted-recipients:; (no To-header on input)
CC:     <g.ottinger@...tec.at>, <eugen.hristev@...rochip.com>,
        <s.etzlstorfer@...tec.at>, Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kees Cook <keescook@...omium.org>, <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] iio: adc: at91: disable adc channel interrupt in timeout case

From: Georg Ottinger <g.ottinger@...tec.at>

Having a brief look at at91_adc_read_raw() it is obvious that in the case
of a timeout the setting of AT91_ADC_CHDR and AT91_ADC_IDR registers is
omitted. If 2 different channels are queried we can end up with a
situation where two interrupts are enabled, but only one interrupt is
cleared in the interrupt handler. Resulting in a interrupt loop and a
system hang.

Signed-off-by: Georg Ottinger <g.ottinger@...tec.at>
---
 drivers/iio/adc/at91_adc.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 75d2f7358..596841a3c 100644
--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -704,23 +704,29 @@ static int at91_adc_read_raw(struct iio_dev *idev,
 		ret = wait_event_interruptible_timeout(st->wq_data_avail,
 						       st->done,
 						       msecs_to_jiffies(1000));
-		if (ret == 0)
-			ret = -ETIMEDOUT;
-		if (ret < 0) {
-			mutex_unlock(&st->lock);
-			return ret;
-		}
-
-		*val = st->last_value;
 
+		/* Disable interrupts, regardless if adc conversion was
+		 * successful or not
+		 */
 		at91_adc_writel(st, AT91_ADC_CHDR,
 				AT91_ADC_CH(chan->channel));
 		at91_adc_writel(st, AT91_ADC_IDR, BIT(chan->channel));
 
-		st->last_value = 0;
-		st->done = false;
+		if (ret > 0) {
+			/* a valid conversion took place */
+			*val = st->last_value;
+			st->last_value = 0;
+			st->done = false;
+			ret = IIO_VAL_INT;
+		} else if (ret == 0) {
+			/* conversion timeout */
+			dev_err(&idev->dev, "ADC Channel %d timeout.\n",
+				chan->channel);
+			ret = -ETIMEDOUT;
+		}
+
 		mutex_unlock(&st->lock);
-		return IIO_VAL_INT;
+		return ret;
 
 	case IIO_CHAN_INFO_SCALE:
 		*val = st->vref_mv;
-- 
2.17.1